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Abstract:

Background: Methylmercury (MeHg) is an environmental contaminant most known for its severe neurotoxic
effects. Although accumulation of MeHg tends to be several folds higher in kidney compared to other
tissues, studies on nephrotoxic effects are almost non-existing. In this study we aim to investigate the
toxicity of dietary MeHg in kidney of Atlantic salmon (Salmo salar).
Material and methods: Atlantic salmon were exposed to dietary MeHg for a period of 8 weeks, before the fish were
euthanized and kidney was sampled for proteomic and real time RT-PCR analysis, as well as for
mercury determination. Protein separation was done with 2-D PAGE, and differentially regulated
spots were picked for analysis using liquid chromatography MS/MS analysis. Moreover, whole blood
and liver tissue were sampled for mercury determination and real time RT-PCR (liver).
Results: MeHg exposed fish accumulated significantly more mercury (Hg) than control fish. The proteomic
analysis revealed differential abundance of 26 spots in the kidney, and 14 of these protein spots
were successfully identified. The proteins identified indicated effects of MeHg on; metabolism,
inflammation, oxidative stress, protein-folding, and cell-structural components. Gene expression
analysis of selected markers revealed few differentially regulated transcripts in kidney and liver in the
exposed fish compared to the control fish. However, the affected transcripts indicated a disruption in
the expression of two metabolic markers due to MeHg exposure in liver.
Conclusion: This study suggests that dietary MeHg has similar effects in kidney as previously shown for other
tissues in fish. The effects observed were in markers for oxidative stress, inflammation and energy
metabolism. The identification of proteomic markers in this study provides a basis for a better
understanding of MeHg-induced nephrotoxicity in fish.